FIELD OF THE INVENTION
The invention relates to a method for ultrasonic leak location, in which sound levels measured at various sites along a measurement segment are represented in a bar diagram, and in which the intersection of two straight lines in the bar diagram is ascertained to identify the location of the leakage. The invention also relates to an apparatus for performing the method.
A method and an apparatus of the above-mentioned type are known from European Patent No. 0 140 174, particularly FIG. 5, and from a brochure entitled "ALUS Acoustical Leakage Monitoring System, Order No. A19100-U653-A212, April 1990, published by Siemens A. G., Energy Production Division, D-91050 Erlangen, Germany.
The method of acoustical leakage monitoring under consideration herein is based on the fact that liquids, vapors or gases produce structure-borne sound as they flow out of a leak and in case of vapors and gases expand. The noises are propagated in affected components (such as pipelines, containers, pumps, valves) and are measured by sound transducers or sound pickups. The latter are mounted at certain intervals on the surface of the components being monitored.
The effective or r.m.s. value E (r.m.s.=root mean square) of the high-frequency sound transducer signals E.sub.HF is used as a measuring variable according to the formula: ##EQU1##
During normal operation, the flow noises generate a background signal level E.sub.o. The sudden occurrence of a leak generates a leakage noise level E.sub.L at a location x.sub.i of the sound transducer (i=1, 2, . . .), having a magnitude which depends on the size of the leak and on its distance from the sound transducer. A total noise level E.sub.L,o at the location x.sub.i of a transducer is the result of superposition of the leakage noise and operating noise, in accordance with the following formula: EQU E.sub.L,O =(E.sup.2.sub.o +E.sup.2.sub.L).sup.0.5. (2)
That means that a leak which generates the same noise level as the operating noise at the location x.sub.i of the sound pickup raises the total noise level by approximately 40%, which is a rise that is readily measurable.
In order to locate the leak, the proportion determined by the leak noise must first be determined for each measuring site x.sub.i, from the sound levels measured by the pickups. That is done in a known way by subtracting the background noise of the system, E.sup.2.sub.o, in accordance with the following formula: EQU E.sup.2.sub.L =E.sup.2.sub.L,o -E.sup.2.sub.o. (3)
The net sound levels E.sup.2.sub.L (or the corresponding values E.sub.L) at the i different locations x.sub.i along the measuring segment are logarithmically shown in a bar diagram and, if a leak is present, the intersection of two straight lines, which will then be present, is utilized to identify the leakage location x.sub.L. (When using the values E.sub.L instead of E.sup.2.sub.L the same final results are obtained.)
In other words, in the method under consideration herein, the operating sound level (r.m.s. value) is monitored for anomalous changes in the ultrasonic range, using a plurality of permanently installed pickups. The frequency range is chosen in such a way that the high-frequency proportions of the leak noise that are above the operating sound level are detected, but the low-frequency, mechanically induced sound waves are filtered out. During normal operation, the r.m.s. values of the various pickups are largely constant. Conversely, leaks cause an increase in the values. Through the use of the known method, the proportion that can be ascribed solely to the leak is determined from that rise for each pickup. That proportion decreases according to the laws of physics as the distance from the leak increases. As was already noted, that proportion is represented logarithmically as a function of the various pickup locations x.sub.i in the form of a bar diagram. Relatively long pipelines or branching pipelines are split up into monitoring segments, and for each segment one such bar diagram is prepared.
The former location method requires constant sound damping along the particular measuring path. Local differences are compensated for by means of special calibration by calculation when use of the method in a system begins. However, experience has shown that when the method is employed in the primary loop of a nuclear power plant, for instance, very great differences arrive in the damping coefficients between the pipelines and individual components of the system (flanges, pumps, steam generators, etc.). Those differences in damping coefficients may amount to a factor of ten or more among one another. Locating is consequently performed with an averaged and therefore locally incorrect damping coefficient, which necessarily leads to defective location of the leak point. Defective location occurs especially if a major change in damping over a short distance is found in the vicinity of the leak point.